[PATCH] D31175: Improve TargetTransformInfo::getCFInstrCost()

[Jonas Paulsson via Phabricator via llvm-commits]

jonpa marked 4 inline comments as done.
jonpa added a comment.

> This is probably true, but it's something I think the TTI implementation might want to worry about, not the vectorizer. The division can be fuzzy, but it's fair to ask TTI about any instruction that will exist in the IR. It's fine for TTI to return 0 (which the default implementation currently does for all branches anyway).

To me it just seems that we should use the information we have at the call site which in this case we know that the branch will most likely not exist in the output.

> I'm not sure I completely understand your question. But I was referring to the branch inside a predicated block (a block contained in PredicatedBBsAfterVectorization).

Ok, now I got it :-)

> So this would ensure that the scalar and vector cases are computed in the same way. Does this make sense?

Yes, that makes sense

I would still vote for that we don't need to ask for a cost of a branch which we know will never exist in output. If we wanted to make it a rule to always make that query, we probably should pass the Instruction pointer as well, so that the cost function can differentiate between different cases or something similar.

Comments anyone?


https://reviews.llvm.org/D31175